DESCRIPTION The studies in this proposal are designed to address specific mechanisms by which embryonic mesenchyme gives rise to a layer of vascular smooth muscle cells, de novo. This morphogenic process occurs during a fifteen hour interval in the quail embryo, an experimental system with many technical advantages for the study of blood vessel formation. The applicant will examine the molecular mechanisms by which vascular smooth muscle precursors become associated with endothelial tubes, and the function of specific integrins in vessel wall morphogenesis. The studies will employ several novel marker proteins for smooth muscle progenitors and their direct descendants. The studies will establish the progression of cell types that lie between primitive mesenchyme and functionally mature vascular smooth muscle cells, and will link specific developmental markers with the progression of atherosclerotic disease. The experimental aims are as follows: Specific Aim 1: Test the hypothesis that the vessel wall is a composite of smooth muscle cells derived from two sources: i) a vascular endothelial cell transformation -- to form an inner layer; and ii) the induction of mesoderm -- to form an outer muscle layer. a. Determine whether an endothelial-mesenchymal transition gives rise to vascular smooth muscle progenitors during normal vasculogenesis. b. Determine whether vascular endothelial cells can recruit smooth muscle precursors from the nearby mesenchyme. c. Determine whether an endothelial-mesenchymal transition gives rise to vascular smooth muscle progenitors during intimal thickening associated with atherosclerosis. Specific Aim 2: To evaluate the function of specific integrins in vivo during smooth muscle cell investment of aortic endothelium. Specific Aim 3: Perform biochemical and molecular characterization of several proteins that, through the use of monoclonal antibodies, have been shown to have a unique pattern of expression associated with the earliest events in vascular morphogenesis.